Magnetic recording and reproducing apparatus

ABSTRACT

In a VTR which provides recording and reproduction of one field video signal the signal is divided into N signal portions with the use of M number of magnetic heads. The signal to be recorded into the nth (n=1, 2, . . . , N) track is delayed by a time (n-1)·T at the recording end and an addition signal of period E is inserted into the blanking period which results from the delaying, and during reproduction or play-back the signal reproduced from the n-th track is delayed by a time (N-n)·d, and is TBC processed, thereby obtaining a composite screen with no skew.

TECHNICAL FIELD

The present invention relates to a magnetic recording and reproducingapparatus for recording and reproducing one field of a video signal withthe signal divided into a plurality of tracks with the use of aplurality of rotation heads, and more particularly to a recording andreproducing system capable of improving the joining of the portions ofvideo signals which appear on the television screen.

BACKGROUND ART

Conventionaly, in a helical scanning type magnetic recording andreproducing apparatus (hereinafter referred to as "VTR"), especially ina VTR for domestic use, a method for recording one field video signal inone track has been utilized. By way of attempting the miniaturization ofthe VTR, a system has been devised in which the number of rotations ofthe rotation drum on which heads are installed is made twice and thediameter of the rotation drum is reduced to a half on an assumption thatthe relative speed of the head and the magnetic tape is not changed,that is, the characteristics of recording and reproducing is notchanged. In this system, one field video of the signal to be recorded isdivided into two tracks, and accordingly there exist two signaljunctions in a field. When one of the signal junctions is placed at thehorizontal blanking period similarly as in the conventional onefield-one track recording system, the other signal junction comes at thecenter of the screen. Accordingly, in order to realize this system it isnecessary to obtain a good junction of video signals at the center ofthe screen, but this is not so simple as will be described below.

Now suppose that an upper half portion and a lower half portion of thescreen are recorded and reproduced by two heads, respectively. Whenthere is a difference in tape tension between at the time of recordingand at the time of reproduction, there arises a time discontinuation inthe head switching position, producing what is called skew. This will bedescribed with reference to FIGS. 4(a)-4(e).

In FIG. 4(a), the reference numeral 2 designates a magnetic tape, thenumerals 3a and 3b designate tracks recorded by the heads 1a and 1b,respectively. If the head 1b is positioned at the position B where therecording is conducted at the same time as at the position A when thehead 1a comes to the head switching point A at the reproduction, thejunction of the signals at the center of the screen is made in a propermanner. This situation is shown in FIG. 4(b). The reference character Pin the drawing represents a signal junction on the screen. However, whenthe position B is deviated to the position B1 caused by the variation inthe tape tension the signal between the position B and B1 will bedropped as shown in FIG. 4(c). Furthermore, when the position B isdeviated to the position B2, the signal between the position B2 and Bwill be repeatedly reproduced as shown in FIG. 4(d). Herein, FIGS. 4(c)and 4(d) shows the amount of skew which is exaggerated for purposes ofexplanation. In an actual VTR the amount of skew is less than ahorizontal scanning period, and when it is received by a televisionreceiver for domestic use, it appears as a curve on the screen by an AFCcircuit having an internal synchronization system as shown in FIG. 4(e).In any event, when a skew occurs, a signal junction at the center of thescreen is visible and undesirable, when viewed.

However, it is quite difficult to eliminate skew in a helical scanningtype VTR. This has been an obstacle in the development of a fielddivision type VTR.

Recently, as a result of the increase in the integration and thedecrease in the cost of integrated circuits as a result of advances insemiconductor technology, it has become possible to correct the skew orjitter by including a digital time axis correction circuit (this isimplemented by a time axis variation detection circuit and a time axisvariation correction circuit, and this is hereinafter referred to as"DTBC") with a VTR. For example, in a DTBC shown in Japanese Laid OpenPatent Publication No. Sho. 58-124385, the detection of the time axisvariation (time axis error) of the input video signal is conducted bydetecting a difference between a sampled phase and a predeterminedphase, which sampled phase is obtained by sampling the input videosignal by a standard clock signal based on a predetermined phaserelationship existing between a predetermined system television videosignal and a local standard clock signal. This correction is conductedin such a manner that the time axis error of the input video signal isdivided into a large error component with a length of one sampling clockperiod as a unit and a small error component which is smaller than asampling clock period, and the former is corrected by adjusting thetiming of the reading out from the shift register properly, and a highpreciseness correction of the latter is conducted by replacing thedriving clock signals for the D/A converter for taking out a correctedoutput video signal or for the input side A/D converter by a signalwhich is obtained by applying a phase modulation to a clock signallocked with a standard synchronous signal in accordance with the timeaxis error.

However, if recording and reproduction are conducted simply in such adevice, signal drops or duplication of signals may arise caused by theskew as described with reference to FIGS. 4(a)-4(e). Especially, when asignal drop arises it is impossible to correct the same even by theDTBC. A well known method to solve this problem will be described below.

FIGS. 5(a) and 5(b) are diagrams for exemplifying the principle of thiswell known method. As shown in FIG. 5(a), at the recording end the videosignals to be recorded of the upper half and the lower half of thescreen are time axis compressed in each track, and at the reproductionend the signals are time extended, i.e. expanded, to restore to theoriginal state. FIG. 5(b) shows a track pattern on the magnetic tape 2.The time axis compressed video signals are recorded at the diagonal linesections E of the tracks 4(a) and 4(b). The reference characters C and Ddesignate the head switching points. Accordingly, signal drops or signalduplications can be avoided by properly establishing a compression rateat the recording properly such that the points C, D and the diagonalline sections E do not cross each other due to the skew.

In this conventional method, however, a large capacity memory of about ahalf field is required and two different kinds of clock frequencies arerequired, whereby the circuit size is undesirably increased.

THE DISCLOSURE OF THE INVENTION

The present invention is directed to solving the disadvantages of theconventional device described above, and has its object to provide a VTRin which one field signal is recorded with divided into N (N is aninteger larger than or equal to 2, independent on N) tracks with the useof M (M is an integer larger than or equal to 1) number of heads, andwhich is capable of correcting distortions on the reproduced screenwithout the use of a large size memory circuit.

According to the present invention, a delay circuit for delaying for thepredetermined time the signals to be recorded into the N tracks and atime axis correction circuit for restoring one field video signal byexecuting a time axis correction to the reproduced signal are providedwith a VTR for recording and reproducing one field video signal with thesignal divided into N tracks with the use of M number of heads.

In the present invention, one field video signal to be divided into Ntracks are delayed by a predetermined time for each track at therecording, respectively, thereby providing blanking periods between thedivided signals on the television screen by sharing the verticalblanking period into the both ends of each track, and at thereproduction the head switching is conducted within the blanking period,and the signal with no signal drops at the signal junction on thetelevision screen is input to the time axis correction circuit, wherebydistortions on the reproduced screen are corrected.

According to the present invention, in recording and reproducing onefield video signal with the signal divided into N tracks with the use ofM number of heads, each signal of the N tracks is delayed by apredetermined time to be recorded, and the vertical blanking period ofthe video signal is shared to the both ends of each track as blankingperiods, and the head switching is conducted in this blanking period,whereby an output video signal with no signal drop on the televisionscreen due to the skew is simply and surely obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) are electrical block diagrams showing theconstructions of the signal processings of the recording system and thereproducing system of a VTR as embodied by the present invention;

FIGS. 2(a)-(e) are diagrams for exemplifying the processes of recordingand reproducing by the VTR;

FIGS. 3a-3c are diagrams showing the track pattern on a magnetic tape ofthe VTR shown in FIG. 1;

FIGS. 4(a)-4(e) are diagrams exemplifying the influence of the time axisvariation in a VTR; and

FIGS. 5(a) and 5(b) are diagrams exemplifying the method of correctingthe time variation in a conventional VTR.

PREFERRED EMBODIMENT OF THE INVENTION

The embodiment of the present invention will be described with referenceto drawings. FIGS. 1(a) and 1(b) broadly illustrate apparatus forprocessing signals in the recording and the reproducing/play-backsections of a VTR system according to the present invention. In thisembodiment the number of the heads M utilized is 2, and the number ofthe screen divisions N is set to 3. That is, the field of the videosignal is recorded into three tracks with the use of two heads.Furthermore, in this embodiment delay line means for delaying the signalreproduced from each track is provided in the reproducing system fordelaying the respective signal by a predetermined time. The dividedsignal portions on the television screen are delayed by these delaylines such that a time axis correction quantity required for restoringthe divided signals stays within the correction ability range of a timeaxis corrector, and thereafter the time axis correction is effected.

Furthermore in this embodiment, an addition signal is inserted into thevideo signal where division processing is executed, and a start positionof the divided video signal is predicted with the use of the additionsignal during signal play-back and reproduction.

In FIG. 1(a), reference numerals 5a, 5b, and 5c designate a first tothird delay line for delaying the input video signal r by apredetermined time, in this instance 0, T, and 2T, respectively. Thereference numerals 6a and 6b designate a switch and a switching signalgenerator therefor for switching the delay lines 5a, 5b, and 5c inaccordance with the position on the screen obtained from the screenposition information of the video signal r. The reference numeral 15designates an addition signal generator. The reference numeral 16designates an adder for adding an addition signal to the video signal.The reference numberal 7 designates an FM modulator. The referencenumerals 8a and 8b designate recording amplifiers provided for thecorresponding two heads 1a and 1b, and the outputs of the recordingamplifier 8a and 8b are coupled to the heads 1a and 1b, respectively.

Furthermore, in the reproducing section (FIG. (1b), reference numerals9a and 9b designate reproduction amplifiers for amplifying the signalsreproduced by the heads 1a and 1b, respectively. The reference numeral10 designates a head swi tch for switching the outputs from thereproduction amplifiers 9a and 9b in accordance with the head positionon the tape. The reference numeral 13 designates a FM demodulator. Thereference numerals 11a, 11b, and 11c designate a fourth to sixth delaylines for delaying the output of the FM demodulator 13 by apredetermined time, in this instance, 2d, d, and 0, respectively. Thereference numerals 12a and 12b designate a switch and a switching signalgenerator therefor for switching the delay lines 11a, 11b, and 11c inaccordance with the position on the screen to be reproduced obtainedfrom the screen position information. The reference numeral 14designates a time axis corrector for detecting the time axis variationof each reproduced signal portion and correcting the time axis variationin accordance with a detected offset. This time axis corrector is wellknown, as shown, for example, in Japanese Laid Open Patent PublicationNo. 58-124385. The reference numeral 17 designates a start positionpredictor for predicting the start position of the video signal bydetecting the addition signal added at the recording end. Furthermore,the reference character S designates the output video signal. Besides,the switching signal generators 6b and 12b can be simply constructedsuch as by a counter which receives the vertical and horizontalsynchronous (synch) signal as screen position information, counts thehorizontal synchronous signals, and is reset by the vertical synchronoussignal, or a horizontal synchronous signal at a predetermined headswitching position.

FIGS. 2(a)-2(e) show the manner of the division and the delay of theinput video signal r in the recording and reproducing process by theapparatus of the embodiment shown in FIGS. 1(a)-1(b). The "upper","middle", and "lower" shown in FIG. 2(a) represent the "upper","middle", and "lower" portion of one field of the television screenobtained by divided the video signal into three parts. The straight linesection represents the blanking period which does not appear on thetelevision screen.

The diagonal line sections shown in FIG. 2(b) and 2(c) shown additionsignals which are generated by the addition signal generator 15 shown inFIG. 1(a) and are added by the adder 16. FIG. 2(e) shows an enlargedview of an example of the addition signal.

FIG. 3 shows a track pattern on a magnetic tape 2. In FIG. 3 thediagonal line sections on the video signal tracks 3a, 3b, and 3c showrecorded portions of signals appearing on the television screen. Thereference characters V to Y designate head switching positions, and theycorrespond to V to Y on the recorded and reproduced signal axis shown inFIG. 2(b).

The device operates as follows.

At the recording end, the input video signal r to be recorded is dividedinto three portions, and the "upper" portion in one field of thetelevision screen is recorded with a delay time of 0 via the first delayline 5a, that is, recorded as is through the FM modulator 7, therecording amplifier 8a, and the head 1a as shown in FIG. 2(b). Next whenthe switching signal generator 6b counts a predetermined number ofhorizontal sync signals a switching signal is generated from thegenerator 6b, whereby the first delay line 5a is switched to the seconddelay line 5b. Accordingly, the signal at the "middle" portion in onefield of television screen is delayed by a predetermined time T, andthereafter it is recorded through the FM modulator 7, the recordingamplifier 8b, and the head 1b as shown in FIG. 2(b). Furthermore, whensignal generator 6b counts a predetermined number of horizontal synchsignals, the second delay line 5b is switched to the third delay line5c. Accordingly, the signal of the "lower" portion in one field oftelevision screen is delayed by a predetermined time 2T, and thereafterit is recorded through the FM modulator 7, the recording amplifier 8a,and the head 1a as shown in FIG. 2(b).

In such a recording method, the blanking period between the "upper"portion and the "middle" portion and the blanking period between the"middle" portion and the "lower" portion become both T in the recordedand reproduced video signal shown in FIG. 2(b). The time T selected suchthat the blanking period Tv between the "lower" portion and the "upper"portion of the next field become larger than the time T.

Thereafter, the same operation is repeated. In this recording method thevertical blanking period in the video signal is shared at both ends ofthe signal on the television screen of each track as a blanking periodas shown in FIG. 3.

In the addition signal generator 15 an addition signal having a period E(E<T) is generated at the latter half of each blanking period as shownin FIG. 2(b). The generation timing of the addition signal is determinedas similarly as the generation of the above-mentioned switching signalin the switching signal generator 6b. The addition signal is added inthe blanking periodd of the video signal by the adder 16 and FMmodulated, and is recorded together with the video signal.

Next, the reproduction operation will be described with reference toFIG. 1(b). At the reproduction end, the signal on a track into which thesignal is recorded by the head 1a, for example, is reproduced by thesame head 1a. In like fashion, the signal on a track into which thesignal is recorded by the head 1b is reproduced by the same head 1b. Theoutputs of the heads 1a and 1b pass through the reproduction amplifiers9a and 9b, respectively, in accordance with the operation of the headswitch 10 which selects the output of the head which is now reproducinga signal on the basis of the head position information received. Theswitching signal generator 12b counts the number of synch signals in thereproduced signal as screen position information, and operates similarlyto the operation of the switching signal generator 6b at the recordingend. Accordingly, the switch 12a is switched so that the signals of the"upper", "middle", and "lower" portions in the television screen passthrough the fourth, fifth, and sixth delay lines 11a, 11b, and 11c,respectively.

Further, as shown in FIG. 2(c) the reproduced signal of the "upper"portion in the television screen is an output which is delayed by apredetermined time 2d by the fourth delay line 11a. The reproducedsignal of the "middle" portion in the television screen is an outputwhich is delayed by a predetermined time d by the fifth delay line 11b,and the reproduced signal of the "lower" portion in the televisionscreen is an output which is delayed by a delay time 0 by the sixthdelay line 11c, that is an, output as is.

The head switching in the above described process is conducted at thepoints V to Y shown in FIG. 2(b) and FIG. 3. That is, the timing of thehead switching is coincident with the periods which are obtained bysharing the vertical blanking periods. If the quantity (T-d-E) which isobtained by subtracting the period of the addition signal E from thedifference between the predetermined delay time T at the recording andthe predetermined delay time d at the reproduction is selected to belarger than a possible maximum skew quantity, and the above-mentioneddelay time d is selected such that the maximum time axis correctionquantity required for restoring the divided signal on the televisionscreen stays within the correction ability range of the time axiscorrector 14, the time axis variations of the output signals of thedelay lines 11a, 11b, and 11c is corrected by the time axis corrector14, and an output video signal S with no signal drop on the televisionscreen due to the skew is obtained as shown in FIG. 2(d).

Next, the use of the addition signal which is added at the recording endwill now be described. Units of the signals are divided with ahorizontal scanning period as described above. Accordingly, the timeaxis variation corrector 14 detects the start position of the dividedvideo signal by detecting the first horizontal synch signal. When it isimpossible to detect the first horizontal synch signal of theabove-mentioned segment caused, such as by a generation of a drop out,there results in a signal drop that arises in a portion of the videosignal because the signal is processed assuming that a blanking signalis reproduced when the next horizontal synchronous signal is detected.The addition signal is used to avoid such a condition. The additionsignal is in a low level state L₀ during the first period e as shown inFIG. 2(e). This state is detected by the start position predictor 17,where it is determined that the reproduction of the addition signal hasstarted. Herein, the period e is established sufficiently wider than thewidth of the horizontal synch signal. Accordingly, the possibility thata signal drop may arise due to, for example, a drop out is decreased toa great extent relative to the horizontal synch signal. Next, in thestart position predictor 17, the transition of the signal level isdetected. That is, the transition points F, G, H, and I between thelevels L₁, L₂, and L₃ which are previously established as shown in FIG.2(e) are detected, and the start position of the video signal ispredicted from the detected result, thereby accounting for a drop of thefirst horizontal synch signal of the segment. In this case, it ispossible to make this prediction with a high degree of precision even ifone point is detected among the four transition points.

In the recording and reproducing process of this embodiment, the droppedportion of the information due to skew is relegated to the blankingperiods and is obtained by sharing the vertical blanking period or tothe addition signal period so that at least the signal on the televisionscreen will not be dropped, since the information during the verticalblanking period, that is, the vertical synch signal is always a wellknown information which occurs with a predetermined regularity.Accordingly, a signal drop of this portion of the signal will raise noproblem if a configuration is adopted wherein a vertical synchronoussignal to be inserted into the output video signal is generated at thereproduction end. Such a configuration is easily obtained.

According to this embodiment, and as evident from the foregoing thesignals of three tracks which constitute one field video signal arerecorded with delays of a predetermined time 0, T, and 2T, respectively.The vertical blanking period is shared at the both ends of each trackand comprises the blanking period and with an addition signal period,and thereby controlling head switching in the blanking period. Drops inthe reproduced signal on the television screen are thereby eliminated,and the generation of skews at a signal junction is obviated.Furthermore, in this invention, a memory of a large capacity as inconventional device is not required, and therefore the apparatus can beobtained at a low cost.

In the above-illustrated embodiment, the respective track signals of onefield video signal which are divided into N tracks are delayed by apredetermined time at the reproduction end so as to reduce the load onthe time axis corrector. The fourth to a sixth delay lines, the switch,and the switching signal generator at the reproduction end can bemodified to achieve the same effects as those of the illustratedembodiment if the correction range of the time axis corrector issufficiently wide.

Furthermore, in the illustrated embodiment the addition signal isrecorded at the recording end and at the reproduction end the startingpoint of a field segment segment is predicted utilizing the additionsignal as a safeguard against a case where the first horizontalsynchronous signal of each segment may drop. The addition signalgenerator, the adder, and the start position predictor can be modifiedto achieve with the same effects as those of the illustrated embodimentif the horizontal synchronous signal is stably reproduced.

What is claimed is:
 1. A magnetic recording and reproducing apparatus ofa helical scanning type for recording and reproducing one field of avideo signal with the video signal being divided into a plurali ty ofsignal portions recorded onto N (N is an integer equal to or greaterthan 2) tracks with the use of M number of heads (M is an integer equalto or greater than 1) which are provided at an interval of 360°/M on arotational drum, comprising: delay line means for delaying the signalrecorded at the recording end into the nth (n=1, . . . , N) track by atime (n-1) T where T is equal to a predetermined time; and time axisvariation corrector means at the reproducing end for correcting the timeaxis variation of each signal reproduced from each of the N tracks andwhich join said signal portions together, thereby restoring said onefield of said video signal.
 2. A magnetic recording and reproducingapparatus as defined in claim 1, and additionally comprising delay linemeans for delaying the signal portion reproduced from the nth (n=1, 2, .. . , N) track at the reproducing end by a time (N-n)·d where d is equalto a predetermined time, and where d<T.
 3. A magnetic recording andreproducing apparatus as defined in claim 2, and additionally comprisingaddition signal generator means at the recording end for generating anaddition signal of a period E in the blanking period where E<T and whichresults from the delay provided by said delay line means, signal addermeans for adding said addition signal to the video signal at therecording end, and start position predictor means at the reproducing endfor predicting the start point of said divided video signal in responseto said addition signal.
 4. A magnetic recording and reproducingapparatus as defined in claim 2, wherein there are provided an additionsignal generator for generating an addition signal of period E (E<T) inthe blanking period which results from the delaying at the recording, anadder for adding said signal, and a start position predictor forpredicting the start point of the divided video signal from saidaddition signal at the reproduction.